In industrial settings, control systems are used to monitor and control industrial and chemical processes, and the like. Typically, the control system performs these functions using field devices distributed at key locations in the industrial process and coupled to the control circuitry in the control room by a process control loop. Field devices generally perform a function, such as sensing a parameter or operating upon the process, in a distributed control or process monitoring system.
Some field devices include a transducer. A transducer is understood to mean either a device that generates an output signal based on a physical input or that generates a physical output based on an input signal. Typically, a transducer transforms an input into an output having a different form. Types of transducers include various analytical equipment, pressure sensors, thermistors, thermocouples, strain gauges, flow transmitters, positioners, actuators, solenoids, indicator lights, and others.
Typically, each field device also includes communication circuitry that is used for communicating with a process control room, or other circuitry, over a process control loop. In some installations, the process control loop is also used to deliver a regulated current and/or voltage to the field device for powering the field device. The process control loop also carries data, either in an analog or digital format.
Traditionally, analog field devices have been connected to the control room by two-wire process control current loops, with each device connected to the control room by a single two-wire control loop. In some installations, wireless technologies have begun to be used to communicate with field devices. Wireless operation simplifies field device wiring and set-up.
One wireless process communication technology standard is known as the WirelessHART® standard. The WirelessHART® standard was published by the HART® Communication Foundation in September 2007. Relevant portions of the WirelessHART® Specification include: HCF_Spec 13, revision 7.0; HART® Specification 65—Wireless Physical Layer Specification; HART® Specification 75—TDMA Data Link Layer Specification (TDMA refers to Time Division Multiple Access); HART® Specification 85—Network Management Specification; HART® Specification 155—Wireless Command Specification; and HART® Specification 290—Wireless Devices Specification.
Another wireless process communication standard is set forth in ISA100.11a (anticipated standard release is August 2009). This technology proposes wireless communication at the 2.4 GHz frequency using radio circuitry in accordance with IEEE 802.15.4-2006. The ISA100.11a standard is maintained by the International Society of Automation (ISA).
While these wireless network communication technologies use the same frequency band, radio circuitry and are configured to coexist in the presence of each other, as well as other wireless technologies at the 2.4 GHz frequency, coexistence is not interoperability. For example, the ISA100.11a standard indicates that coexistence is the ability of a wireless network to perform its task in an environment where there are other wireless networks that may not be based on the same standard. As used herein, two networks that are not based on the same standard will be considered “distinct” networks.